In the prior art, voltage controlled oscillators (VCOs) generally require a large number of components to form the various parts required for oscillation and control. For example, generally inductors and capacitors are required to form a tank, or resonant, circuit and additional components are required to change the resonant frequency. At least one of these components must change with the application of a voltage so that the resonant frequency can be varied. Specifically, in a varactor oscillator, the varactor operates like a capacitor (provides capacitance) which varies in accordance with the voltage applied across the varactor. In other oscillators resonance is provided by tuned magnetic circuits but many components are still required to provide the voltage control.
In a copending United States Patent Application entitled "Dual Voltage Controlled Oscillator and Method of Operation", filed Jul. 1, 1996, with Ser. No. 08/673,879, now U.S. Pat. No. 5,708,398, and assigned to the same assignee, a VCO is disclosed which uses a single negative differential resistance (NDR) device in series with a transistor to produce a novel VCO. It is, however, desirable to produce an improved VCO with a wider tuning range which can be used, for example, in communication equipment such as transmit/receive modules.
Accordingly, it is a purpose of the present invention to provide a new and improved oscillator with wider tuning range.
It is another purpose of the present invention to provide a new and improved oscillator with wider tuning range which is simple to fabricate and which includes a minimum of components.
It is still another purpose of the present invention to provide a new and improved oscillator with wider tuning range which can be fabricated on a single substrate.
It is a further purpose of the present invention to provide a new and improved voltage controlled oscillator with wider tuning range which is integrated into a single device.